iPhone HEIC to JPG

On the iPhone, open Settings, Camera, Formats. If High Efficiency is on, new pictures are HEIC. To send a JPG without changing that setting, copy the photo to a computer and convert it here.

AirDrop to a Mac, or plug the phone in and copy the .heic file. Then use the HEIC to JPG tool below. Most Efficient and High Efficiency both produce HEIC files.